1. Field of the Invention
The present invention relates to a voltage fluctuation compensating apparatus for detecting and compensating a voltage dip when voltage of an electric power system supplied to a load dips instantaneously.
2. Description of the Related Art
In some cases, voltage of an electric power system may dip instantaneously due to lightning so that a precision machine in a factory malfunctions or stops temporarily to cause great damage in a production line. In order to prevent such damage, there is used a voltage fluctuation compensating apparatus for monitoring voltage fluctuation such as an instantaneous voltage dip in an electric power system, and compensating the voltage dip.
FIG. 18 is a schematic configuration diagram showing a related-art voltage fluctuation compensating apparatus. As shown in FIG. 18, electric power from a power line 1 is stepped down by a transformer 2, and then connected to a customer 3 (load) through a voltage fluctuation compensating apparatus. Thus, electric power is supplied to the customer 3. The voltage fluctuation compensating apparatus includes a DC power source 4, an inverter 5, a smoothing filter 6, and a high-capacity transformer 7.
Description will be made below about the voltage compensating operation in such a related-art voltage fluctuation compensating apparatus at the time of an instantaneous dip of a system voltage.
FIG. 19 shows a system voltage, an output of a voltage fluctuation compensating circuit, and a voltage supplied to the customer 3, respectively, at the time of an instantaneous dip of a system voltage. As shown in FIG. 19, when a voltage dip occurs instantaneously in the system voltage, the voltage dip is detected by a detection unit (not shown) which monitors voltage fluctuation. By the power feeding control based on the detected voltage dip, an AC voltage is generated by the DC power source 4 and the inverter 5 in the voltage fluctuation compensating apparatus. The AC voltage is connected in series to the power system through the smoothing filter 6 and the high-capacity transformer 7. Thus, the voltage dip of the power system is compensated. As a result, the output voltage from the voltage fluctuation compensating apparatus is added to the system voltage in which the voltage dip has occurred, so that electric power with a normal voltage is supplied to the customer 3.
Since the related-art voltage fluctuation compensating apparatus is configured thus, the system voltage flows into the inverter 5 through the transformer 7 correspondingly to a load current even when the system voltage is normal. As a result, loss by the transformer 7 and the inverter 5 occurs even at the normal time. Thus, a large-scale cooling unit is required.
In addition, since a voltage is supplied to the power system through the smoothing filter 6 and the transformer 7 at the time of an instantaneous dip of the system voltage, the capacities of the smoothing filter 6 and the transformer 7 becomes high. Thus, there has been a problem that the apparatus increases in size.
The invention has been made to solve the foregoing problems. An object of the invention is to obtain a voltage fluctuation compensating apparatus which can carry out voltage compensation with high accuracy at the time of an instantaneous dip of the system voltage, and which can be arranged as a whole at low cost and in a small size.
According to the invention, there is provided a voltage fluctuation compensating apparatus for suppressing fluctuation of a voltage supplied to a load. The voltage fluctuation compensation apparatus includes a detection/control portion, and a plurality of voltage compensating circuits.
The detection/control portion monitors a voltage dip in a power system, and controls power feeding in accordance with a result of the voltage dip monitoring.
The voltage compensating circuits is connected in series to the power system. The voltage compensating circuits includes a plurality of energy storage units (capacitors) respectively having charging voltage values different from one another and in relationship of approximately 2k-fold (K=0, 1, 2, . . . ) with respect to a smallest charging voltage value (absolute value) of the charging voltages. The voltage compensating circuits convert DC voltages charged in the capacitors into AC voltages and outputs the AC voltages, respectively.
The charging voltage values of the capacitors respectively in the voltage compensating circuits are used as bit signals for a reference value to check a voltage dip amount of the power system with the reference value and A/D convert the voltage dip amount into a binary signal. The desired combination is selected from the plurality of voltage compensating circuits in accordance with the binary signal so that a total sum of output voltages of the selected voltage compensating circuits compensates for the voltage dip of the power system.